Obstructive sleep apnea (OSA) is a category of sleep-disordered breathing, which involves a disturbance of respiratory patterns during sleep. Typically, muscle tone in the body relaxes during sleep. In the throat, the airway has collapsible walls of soft tissue, which can obstruct breathing during sleep.
OSA is frequently undiagnosed, where the prevalence increases generally with age, however OSA is known to exist among African Americans, individuals with low muscle tone and soft tissue around the airway, and individuals with structural features resulting in a narrowed airway. The upper airway depends on the soft and bony tissue in the pharynx. The obstruction can occur anywhere along the naso- and oro-pharynx. Typically, OSA is primarily due to obstruction from the tongue falling back during sleep and occluding the airway, the soft palate laxity or a combination of both. Most OSA can be attributed to the tongue. The elderly are more likely to have OSA than young people. Men are more typical sleep apnea sufferers, however women and children are also affected.
Factors that contribute to OSA include obesity (especially neck circumference), upper airway anatomic abnormalities, smoking, and chronic nocturnal nasal congestion. Symptoms include awakening with choking or gasping, restless sleep, episodes of cessation of breathing, loud snoring, morning headaches and sleepiness during the daytime. The most serious complication is a severe form of congestive heart failure.
Sleep apnea is diagnosed with an overnight sleep study (polysomnography), which monitors patients for evaluating sleep stages, respiratory effort, airflow, arterial oxygen saturation, cardiac rate and rhythm, body position, and limb movements. Diagnosis is made with greater than 15-apneas and/or hypopneas (Apnea Hypopnea Index AHI) per hour of sleep without symptoms, or greater than 5-apneas/hypopneas per hour with symptoms. Patients with OSA, in the long term, have increased association with myocardial infarction, cerebrovascular disease, arrhythmias, and sudden cardiac death. OSA has been directly linked with systemic hypertension, pulmonary hypertension and motor vehicle accidents.
Chronic, severe obstructive sleep apnea requires treatment to prevent sleep deprivation and other complications. Some treatments involve lifestyle changes, such as avoiding alcohol or muscle relaxants, losing weight, and quitting smoking, but changing behavior is often difficult in the setting of OSA. One treatment requires sleeping at a 30-degree elevation of the upper body or higher, as if in a recliner in an attempt to prevent the gravitational collapse of the airway. Another treatment is the use of a continuous positive air pressure (CPAP) machine. The CPAP machine delivers a stream of compressed air via a hose to a nasal pillow, nose mask or full-face mask, keeping the airway open under air pressure so that unobstructed breathing becomes possible, reducing and/or preventing apneas and hypopneas. However, a significant number of patients cannot tolerate CPAP because of the mask, noise, sensation of airflow, and dry mucosa from the airflow. Oral appliances have been used to hold the tongue or advance the mandible and so directly effect causes of obstruction. These appliances have been shown to improve OSA but they are poorly tolerated. Oral appliances are also thought to be less effective than CPAP.
There are also invasive surgical procedures to remove and tighten tissue, and to widen the airway. Uvulopalatopharyngoplasty (UPPP), palate support pillars, Radiofrequency (RF) ablation (Gyrus ENT), tongue suspension, genioglossus advancement, and maxillary-mandibular advancement have all been tried with variable success. Genioglossus and maxillary-mandibular advancement is very effective but invasive and uncomfortable often leading to changes in facial appearance and speech. UPPP can be effective in a subset of patients and is often used in conjunction with other treatments. Tongue suspension (Repose) is effective in the short term but loses efficacy after one year. Palate support pillars are also useful in only a limited subset of patients. Radiofrequency ablation has great promise in the past but comfort and efficacy have been limited due to the need to deliver RF current at multiple sites over several separate procedures using a painful needle. In conventional RF ablation configurations, the current density is highest at the ablation electrode. The ohmic heating occurs at the tissue-electrode interface and then the heat is transferred to the surrounding tissue through thermal conduction. In order to ablate (and therefore debulk and stiffen) the tongue, the Gyrus device uses ablation “needles” to penetrate and deliver energy to the tongue's interior. If the RF current, using a conventional setup, is delivered from the tongue's surface, the patient receives painful burns on the surface of the tongue before getting significant heating and debulking of the organ. Even with extensive surface cooling at the electrode interface, surface burns can occur in order to achieve interior target temperatures.
What is needed is a comfortable, minimally invasive and effective long-term device and method to non-invasively change the properties inside a volume of tissue, especially the tongue to treat obstructive sleep apnea.